A literature survey identified 403 primary research publications that investigated the ecological effects of invasive alien insects and/or the mechanisms underlying these effects. The majority of these studies were published in the last 8 years and nearly two-thirds were carried out in North America. These publications concerned 72 invasive insect species, of which two ant species, Solenopsis invicta and Linepithema humile, accounted for 18% and 14% of the studies, respectively. Most publications investigated effects on native biodiversity at population or community level. Genetic effects and, to a lesser extent, effects on ecosystem services and processes were rarely explored. We review the effects caused by different insect invaders according to: their ecosystem roles, i.e. herbivores, predators, parasites, parasitoids and pollinators; the level of biological organisation at which they occur; and the direct and indirect mechanisms underlying these effects. The best documented effects occur in invasive ants, Eurasian forest herbivores invasive in North America, and honeybees. Impacts may occur through simple trophic interactions such as herbivory, predation or parasitism. Alien species may also affect native species and communities through more complex mechanisms such as competition for resources, disease transmission, apparent competition, or pollination disruption, among others. Finally, some invasive insects, particularly forest herbivores and ants, are known to affect ecosystem processes through cascading effects. We identify biases and gaps in our knowledge of ecological effects of invasive insects and suggest further opportunities for research.

Ecological effects of invasive alien insects

Multi-function agricultural biodiversity: pest management and other benefits

Invasive species threaten natural habitats worldwide, and active human management is required to prevent invasion, contain spread, or remediate ecosystems following habitat degradation. One powerful technology for invasive species management in sensitive habitats is biological control, the use of carefully se- lected upper-trophic-level organisms that utilize the exotic pest as a resource, thereby reducing it to less harmful densities. Many in the conservation biology community view this pest-management technology as a high-risk enterprise because of potential collateral damage to nontarget species. The potential benefits arising from suc- cessful biological programs are reduced pesticide use, significant pest suppression, and a return to ecological conditions similar to those observed before the arrival of the pest. Biological control as a pest-management strategy has limitations: some pest species may not be suitable targets for biological control because natural enemies may not be sufficiently host-specific and may pose a threat to nontarget organisms. In some instances, substantial effects on nontarget species have occurred because generalist natural enemies established as part of a biological control program heavily utilized other resources in addition to the target pest. To minimize nontarget impacts, regulations governing releases of natural enemies are becoming more stringent, as evi- denced in New Zealand and Australia. Voluntary codes of good practice are being advocated by the Food and Agriculture Organization to promote wide adoption of safety measures, which, if followed, should result in the selection of agents with high levels of host and habitat fidelity. Biological control programs in support of con- servation have traditionally targeted weed species that threaten natural areas. More recently, exotic arthropod pests that compete with native wildlife or damage native plants have become targets of conservation-oriented biological control programs. Extension of biological control to new targets of conservation importance, such as invasive aquatic invertebrates and pestiferous vertebrates, is warranted. In many instances, once prevention, containment, and eradication options have been exhausted or deemed infeasible, carefully orchestrated bio- logical control programs against appropriately selected targets may be the only feasible way to control invasive species affecting communities under assault from exotic species.

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Restoring Balance: Using Exotic Species to Control Invasive Exotic Species

1. As ectothermic organisms, butterflies have widely been used as models to explore the predicted impacts of climate change. However, most studies explore only one life stage; to our best knowledge, none have integrated the impact of temperature on the vital rates of all life stages for a species of conservation concern. 2. Besides, most population viability analysis models for butterflies are based on yearly population growth rate,precluding the implementation and assessment of important climate change scenarios, where climate change occurs mainly, or differently, during some seasons. 3. Here, we used a combination of laboratory and field experiments to quantify the impact of temperature on all life stages of a vulnerable glacial relict butterfly. Next, we integrated these impacts into an overall population response using a deterministic periodic matrix model and explored the impact of several climate change scenarios. 4. Temperature positively affected egg, pre-diapause larva and pupal survival, and the number of eggs laid by a female ; only the survival of overwintering larva was negatively affected by an increase in temperature. Despite the positive impact of warming on many life stages, population viability was reduced under all scenarios, with predictions of much shorter times to extinction than under the baseline (current temperature situation) scenario. Indeed, model predictions were the most sensitive to changes in survival of overwintering larva, the only stage negatively affected by warming. 5. A proper consideration of every stage of the life cycle is important when designing conservation guidelines in the light of climate change. This is in line with the resource-based habitat view, which explicitly refers to the habitat as a collection of resources needed for all life stages of the species. We, therefore, encourage adopting a resource-based habitat view for population viability analysis and development of conservation guidelines for butterflies, and more generally, other organisms. Life stages that are cryptic or difficult to study should not be forsaken as they may be key determinants in the overall response to climate change, as we found with overwintering Boloria eunomia larvae.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2656.2012.02029.x

Each life stage matters: the importance of assessing the response to climate change over the complete life cycle in butterflies

Biological control is the suppression of populations of pests and weeds by living organisms. These organisms can provide important protection from invasive species and protect our environment by reducing the need for pesticides. However, they also pose possible environmental risks, so biological control interventions must be undertaken with great care. This book enhances our understanding of biological control interactions by combining theory and practical application. Using a combination of historical analyses, theoretical models and case studies, with explicit links to invasion biology, the authors cover biological control of insects, weeds, plant pathogens and vertebrate animals. The book reflects increasing recognition of risks over the past 20 years, and incorporates the latest technological advances and theoretical developments. It is ideal for researchers and students of biological control and invasion biology.

Biological Control: Ecology and Applications

Non-target parasitism of the endemic New Zealand red admiral butterfly (Bassaris gonerilla) by the introduced biological control agent Pteromalus puparum

1 Eighty four-unit domiciles for introduced bumble bees (Bombus spp) were placed in 16 field margins at Lincoln, New Zealand in the 1995–96 southern summer Fifty-five were placed in the margins of intensively managed fields, with the remaining 25 being in less disturbed habitats, which had more spring/summer floral resources

2 The number of nests founded over the four-year study period increased from one to 27 Bombus hortorum was a much more frequent colonist than was B terrestris, with B ruderatus colonizing only in the fourth year

3 In the ‘intensive’ sites, mean four-year occupancy was only 2%, whereas in the less disturbed sites it was 13%

4 There was a positive association between bumble bee occupancy of the domicile compartments in the previous year and occupancy in the current year No association was found between previous occupancy by mice and subsequent occupancy by bumble bees

5 The potential for adding Bombus nest sites to agricultural land to enhance local populations, and, potentially, pollination of seed crops, is discussed Adding domiciles in intensively managed landscapes may not be very effective unless spring floral resources are enhanced as well

A four‐year investigation into the efficacy of domiciles for enhancement of bumble bee populations

Retrospective modelling indicates minimal impact of non-target parasitism by Pteromalus puparum on red admiral butterfly (Bassaris gonerilla) abundance

This study examined whether two species of lepidopteran larvae (Cleora scriptaria and Epiphyas postvittana) were deterred from feeding on the leaves of kawakawa (Macropiper excelsum) after the leaves had been damaged in three different ways: by larval feeding, using a hole punch or a metal rasp. A hierarchy of choice experiments was performed in the laboratory, examining the feeding 'preference' of these insects between undamaged or previously damaged tissue within the same leaf, between different leaves and between different plants. On no occasion did larvae of either species show a significant preference for undamaged or damaged leaves. It is concluded that, on present evidence, kawakawa does not have a system of induced chemical defences which deters the feeding of these two insects.

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M.C. Barron

Papers

Non-target parasitism of the endemic New Zealand red admiral butterfly (Bassaris gonerilla) by the introduced biological control agent Pteromalus puparum

A four‐year investigation into the efficacy of domiciles for enhancement of bumble bee populations

Retrospective modelling indicates minimal impact of non-target parasitism by Pteromalus puparum on red admiral butterfly (Bassaris gonerilla) abundance

Induced defences in kawakawa (Macropiper excelsum): do caterpillars avoid previous leaf damage?